When I use the Custom Menu Widget in a side bar it looks great on the desktop and iPad. But it breaks on a smartphone like the iPhone. On the iPhone, the Sidebar Custom Menu box appears on the page, but it's empty, no nav links. I suspect, that because the mobile nav includes a list of all the site pages, then such custom menus for lower level sections are not needed, so they don't appear. But if that's the case, then the menu box should not appear either. Seems to be a bug.
If indeed the mobile menu includes all site pages as it appears, then is there a way to hide the custom menu box as well when the page is viewed on an iPhone or equivalent?